A commutating forward lamp driving circuit is advantageously used for operating high intensity discharge (HID) lamps. In a forward commutating lamp driving circuit, a down-converter (forward converter) and a commutation circuit (inverter) are combined. Such a lamp driving circuit may be embodied in a half-bridge commutating forward (HBCF) topology or a full-bridge commutating forward (FBCF) topology.
Besides driving the discharge lamp in a steady state by providing a suitable lamp current, the lamp driving circuit needs to be configured for igniting the discharge lamp, requiring a high voltage. In particular, metal halide discharge lamps may extinguish after ignition due to e.g. electrode conditions. Therefore, preferably a lamp driving circuit is configured for fast re-ignition of an extinguished lamp without separate control such as used when using a pulse igniter as known from the prior art.
U.S. Pat. No. 6,380,694 discloses a HID lamp driving circuit. The lamp driving circuit uses two switching devices and an inductor/capacitance filter in a high frequency resonant mode to ignite the lamp. The high frequency resonant mode is continued for a predetermined period of time to provide a smooth transition from a glowing condition to an arcing condition. A further inductance/capacitance filter operates as a high frequency ripple-reducing filter for reducing a high frequency ripple in a lamp current during steady state operation. In the steady state operation a first set of switching devices is alternately controlled at a first high frequency, while a second set of switches is alternately controlled at a second low frequency.